The invention relates to measuring probes for measuring and taking samples with a metal melt, the probe having a measuring head arranged on a lance, wherein the measuring head carries at least a temperature sensor and a sampling chamber, and wherein the sampling chamber is surrounded by the measuring head and includes an intake duct made of a quartz glass tube that extends through the measuring head.
Measuring probes of this type are known in principle and are used, among other uses, in steel-making in so-called converters or in electric arc furnaces.
In a converter (so-called BOF converter—technical term for basic oxygen furnace), a lance is used to blow oxygen into the metal melt. The converter is lined with refractory material, which withstands the erosion due to slag and heat during the oxygen blowing process in an optimal manner. Scrap metal and limestone (calcium oxide) are added into the converter in order to cool the melt and remove phosphorus, silicon, and manganese. The oxygen combusts the carbon to form carbon monoxide and carbon dioxide. Manganese, silicon, and phosphorus are oxidized and converted in the presence of calcium oxide and iron oxide to form slag.
Since the oxidation reaction is highly exothermic, the process needs to be cooled in order to control the temperature of the melt. Cooling is effected by adding scrap metal and iron ore during the blowing process. The oxygen blowing process itself takes approx. 15-20 minutes to complete, independent of the size of the converter, which can be approximately 70-400 tons. In this context, the oxygen flow rate of the lance is adapted to the size of the converter and/or the weight of the melt. Loading and unloading steel and slag including measuring the temperature and taking samples for analysis of the melt leads to a time period of 40-60 minutes between 2 tapping stages.
The overall process is characterized by its high productivity and leads to a steel with a low content of contaminations. In the tapping stage, the furnace is tilted and the product poured through a tapping hole into a casting ladle. During this operation, iron alloys are added into the casting ladle to control the steel composition. One important development of the oxygen blowing lance technique is to add inert gas, usually argon, through the converter floor to the melt, in order to stir the melt and the slag. This process increases the efficiency considerably, and both the iron loss and the phosphorus content decrease. Moreover, the heat and mass equilibrium of the process is improved, which reduces the costs.
Measuring probes for use in the converter are described, for example, in German Patents DE 10 2005 060 492 B3 and DE 10 2005 060 493 B3.
In an electric arc furnace, scrap metal is melted by the energy of an electric arc, which is generated between the tips of graphite electrodes and the conductive scrap metal load. For loading the scrap metal in the furnace, the three electrodes and the roof of the furnace are lifted up to expose a filler hole. The electrodes maintain the electric arc in accordance with the pre-selected voltage and pre-selected current, thus providing the energy required for melting and oxidizing. Electric arc furnaces have an internal diameter of approx. 6-9 meters and a capacity of 100-200 tons of steel. The time between two tapping stages in the furnaces is usually approx. 90-110 minutes.
Measuring probes for use in electric arc furnaces are known, for example, from German Patents DE 28 45 566 C2 and DE 103 60 625 B3, and German published patent application DE 32 03 505 A1.
For monitoring the processes in the converter or electric arc furnace, it is necessary to completely fill the sampling chamber of a measuring probe at relatively low temperatures in the process of taking a sample, whereby gas bubbles in the sample should be prevented. This type of taking a sample is not always easy, in particular during the blowing process in the converter, since the theoretical density of the steel melt varies strongly, on the one hand, due to the oxygen blowing process from above and, on the other hand, due to inert gas being blown in through the converter floor. Moreover, the industry tends to use furnaces that permit only little overheating of the melt (that is to say, only a small difference between the bath temperature and the liquidus temperature).